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[dm-devel] Re: IO scheduler based IO Controller V2

On Mon, May 11, 2009 at 08:23:09PM +0900, Ryo Tsuruta wrote:
> Hi Vivek,
> From: Vivek Goyal <vgoyal redhat com>
> Subject: Re: IO scheduler based IO Controller V2
> Date: Wed, 6 May 2009 21:25:59 -0400
> > On Thu, May 07, 2009 at 09:18:58AM +0900, Ryo Tsuruta wrote:
> > > Hi Vivek,
> > > 
> > > > Ryo, dm-ioband breaks the notion of classes and priority of CFQ because
> > > > of FIFO dispatch of buffered bios. Apart from that it tries to provide
> > > > fairness in terms of actual IO done and that would mean a seeky workload
> > > > will can use disk for much longer to get equivalent IO done and slow down
> > > > other applications. Implementing IO controller at IO scheduler level gives
> > > > us tigher control. Will it not meet your requirements? If you got specific
> > > > concerns with IO scheduler based contol patches, please highlight these and
> > > > we will see how these can be addressed.
> > > 
> > > I'd like to avoid making complicated existing IO schedulers and other
> > > kernel codes and to give a choice to users whether or not to use it.
> > > I know that you chose an approach that using compile time options to
> > > get the same behavior as old system, but device-mapper drivers can be
> > > added, removed and replaced while system is running.
> > > 
> > 
> > Same is possible with IO scheduler based controller. If you don't want
> > cgroup stuff, don't create those. By default everything will be in root
> > group and you will get the old behavior. 
> > 
> > If you want io controller stuff, just create the cgroup, assign weight
> > and move task there. So what more choices do you want which are missing
> > here?
> What I mean to say is that device-mapper drivers can be completely
> removed from the kernel if not used.
> I know that dm-ioband has some issues which can be addressed by your
> IO controller, but I'm not sure your controller works well. So I would
> like to see some benchmark results of your IO controller.

Fair enough. IO scheduler based IO controller is still work in progress
and we have started to get some basic things right. I think after 3-4
iterations of patches, patches will be stable enough and working enough that
I should be able to give some benchmark numbers also.

Currently I am posting the intermediate snapshot of my tree to lkml to get the
design feedback so that if there are fundamental design issues, we can sort
these out.


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